Firstly, there's no reason why you can't mix tenses in a sentence. Did a teacher or textbook say that you can't? If a doctor asks you how much you exercise, you can say 'I walk 2 km every morning and ran 1 km yesterday'.
Secondly, may and might are modal verbs, and most of the rules about verb tenses don't apply to modal verbs. There are times when can functions as present tense and could as past tense: 'I can walk 2 km every day and could run 1 km when I was young'. But there are other times when can means ability and could means possibility: 'I can get to your party at 8 pm, and could arrive earlier'.
May and might really don't function as present and past tense like can and could can, and in most cases, they both function as the same 'tense' and both mean possibility. If there's a difference, it is that may is slightly more likely and might is slightly less likely: 'I may get to you party at 8 pm, and might arrive earlier'.
Using 'might have' and 'may' (or 'may have' and 'might') doesn't really change this. 'Might have' is still the same 'tense' as 'might' (and 'may'), even if we are now talking about the past.
As Ronald Sole said in his comment, 'it's a mouthful of a sentence'. Don't say or write sentences like this too often, just because it's possible.
Last thought: Why don't you simply say "I have changed"? You might not know if someone else has changed, but you surely know whether you have or haven't. I would probably say or write 'To your pleasure, I have changed, and might not dwell in silly thoughts about love (as/like) I used to a few years ago'. (I don't use 'may' as often as 'might'.